Move from Unsubscribe to Active/Unconfirmed using c#

If you're using our .Net API wrapper (http://campaignmonitor.github.io/createsend-dotnet/), then it's quite easy. You just need to call one of the Add or Update methods from the Subscriber class (https://github.com/campaignmonitor/createsend-dotnet/blob/master/createsend-dotnet/Subscriber.cs), with the resubscribe parameter set to true.

If you're not using our .Net API wrapper, then all you need to do is make a call to the Add or Update end points (https://www.campaignmonitor.com/api/subscribers/), with the resubscribe parameter set to true.